This invention relates to the field of dynamoelectric machines which utilize a liquid as a cooling means, and particularly induction motors of the so-called "squirrel-cage" configuration. The present invention is an improvement over liquid cooled electrical machines such as those disclosed by U.S. Pat. No. 3,480,810 issued Nov. 25, 1969 to Potter which direct cooling fluid to a location adjacent heat producing rotor elements and depend upon the thermal conductivity of the rotor structure to conduct heat away from the primary heat source and to the liquid.
Electrical machines consist primarily of a rotor and a stator which both contain heat producing conductors. To increase rotor and stator current, and the efficiency of these machines, it is necessary to provide means to remove the heat produced by the resistance of the conductors to current flow. To this end, induction motors in the past have been cooled by forcing air through the rotor slots and around the rotor exterior. The drawback of these systems has been that heat transfer between the heat producing conductors and the air was not sufficient to provide adequate cooling.
Liquid cooling has been proposed, as in Potter above, but these attempted solutions have not proven adequate for one of two reasons. First, if cooling liquid is allowed to enter the gap between the rotor and the stator, more efficient cooling may result but increased rotational drag losses cause unacceptable power losses. Second, systems which prevent liquid from entering the gap between the rotor and the stator have done so by channeling cooling fluid to only a limited portion of the rotor and relying upon conductor support structure to transfer heat from the rotor conductors to the cooling liquid. Such systems decrease power losses but do not reach heat transfer efficiencies which would be possible if the cooling liquid were in contact with the heat source.